Valve cover says max rpm 4600-5000. So what do I need to do to change the gearing? Or how do I verify the gear ratio for sure? Is changing gears the solution?

Or.... Would that taller gear be good for say a.... Simple procharger setup and then the 23pitch or so prop??
Just looking at all options since I have a little better motor than original discussed

Single engine boats don't work real well with tall outdrive ratios until you start making real big hp, mine with 1000 didn't really like the 1.36's when I tried them (less tq multiplication). Pull your drive off, shift it into gear and count how many turns it takes the input to make output turn exactly once, if you haven't had it off it would be a good time for you to inspect the u-joints, splines and coupler, Smitty

You might be able to find your drive and ratio on this chart but that doesn't mean someone hasn't thrown some other gears in, count the input vs 1 turn of the output is best way without dissassembling
http://www.mercruiserparts.com/Show_...IVE+UNIT+CHART

Alright I will have to do some research on this process I suppose as I'm new to this, is it correct I'm seeing gear sets for under 300$ to switch to a 1.5 drive ratio?

More like 500-600 for the gears. Its no do it yourself job, so figure the same money for the labor.

Where are you seeing gear sets for that price? You can buy a complete chinese lower with 1.50 gears (15/39) for 895$ all brand new, if you have a good merc lower with decent gears you could sell it used for 1/2 that and have all brand new , I'm not real fond of Chinese crap and giving them money but it is a option, Smitty

Yeah, but if you run the numbers with the 23 @4200rpms and a 1.5 ratio, they come out correct at 15% which is pretty typical for a 24 OL.

I saw that too but my reasoning is he could be slipping that 23 because its so tall-maybe trimmed too high not sure but there is no way he could get the slip to zero with a 20 pitch IF his numbers are correct-4600/58mph with 20 pitch. A guy was on here recently saying his boat only went x speed with x prop and when I crunched his slip numbers it was below zero and he swore what he was saying was true so its hard to help someone sometimes without seeing this stuff in person, Smitty

The numbers are based off my gps speedo and mechanical tach, I can hook my timing light up and check the rpm with it, there is no real GOP stamp or anything on that power tech prop I will get all the numbers on it and check what I can. As far as replacing the gears or whatever if I need to I don't want cheap junk or whatever I want to do it right but also don't have the desire to spend 4-5,000 on a lower ill just leave it be if that's the case. As far as the numbers with the 23P prop it was trimmed all the way up to get it to rev to 4200, I use my power trim gauge a lot and with the 20 I have to leave it pretty low in the water to keep it from porpoising but with the 23 it was shooting a pretty good roost and trimmed all the way up and still no porpose but it would only get to 4200 rpm and it BARELY got on plain